Admixture, extrudable hydraulic composition and method for the selection of admixture

ABSTRACT

A nonionic water-soluble cellulose ether is characterized in that when 3 pbw of the nonionic water-soluble cellulose ether is added to a mixture of 90 pbw of cordierite, 10 pbw of ordinary Portland cement, and 33 pbw of water, immediately followed by kneading at 20° C. and 20 rpm, a maximum torque for kneading is reached within 180 seconds from the addition. It is suitable as an admixture for extrudable hydraulic compositions. The hydraulic composition to which the inventive admixture is added can be kneaded within a brief time into a uniform mass which is smoothly extrudable.

TECHNICAL FIELD

[0001] This invention relates to an admixture which enables anextrudable hydraulic composition to be kneaded into a uniform masswithin a short time, an extrudable hydraulic composition comprising thesame, and a method for selecting a nonionic water-soluble celluloseether suitable as the admixture.

BACKGROUND OF THE INVENTION

[0002] In traditional hydraulic compositions for extrusion molding,asbestos were used as additive fibers for facilitating extrusion intohardened parts having surface smoothness. In the recent years, theamount of asbestos used drastically decreased due to healthconsiderations and legal regulations. At present, pulp fibers are oftenused as the substitute. In unison with this tendency, nonionicwater-soluble cellulose ether is commonly used for the purposes ofimproving the dispersion of pulp fibers, enhancing strength propertiesand facilitating extrusion.

[0003] As the avoidance of asbestos is in progress, the amount ofnonionic water-soluble cellulose ether used is increasing. Thisincreases the cost of extruded parts, preventing widespread use thereof.

[0004] Extrudability depends on the solubility of a nonionicwater-soluble cellulose ether used. On use of a nonionic water-solublecellulose ether having a slow dissolution rate, a longer time ofkneading is needed or the amount of the cellulose ether must beincreased. These drawbacks also increase the cost of extruded parts,preventing widespread use thereof.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide an admixturecomprising a nonionic water-soluble cellulose ether, which permits anextrudable hydraulic composition to be obtained by brief kneading ofnecessary components with a reduced amount of the nonionic water-solublecellulose ether and hence, at a low cost, the composition beingeffectively extrudable into hardened parts of quality. Another object isto provide an extrudable hydraulic composition comprising the admixture.A further object is to provide a method for selecting a nonionicwater-soluble cellulose ether suitable for use as the admixture.

[0006] The inventor has found that a nonionic water-soluble celluloseether which is characterized in that a maximum torque (or torque peak)for kneading at 20° C. and 20 rpm immediately after addition of thenonionic water-soluble cellulose ether to a mixture of cordierite,ordinary Portland cement, and water is reached within 180 seconds fromthe addition is effective as an admixture; that an extrudable hydrauliccomposition to which the admixture is added can be finished by briefkneading of necessary components, even with a reduced amount of thenonionic water-soluble cellulose ether; and that this hydrauliccomposition can be uniformly and smoothly extruded into hardened partswith a satisfactory outer appearance.

[0007] The inventor made a study on the nonionic water-soluble celluloseether which when added as an admixture to a hydraulic composition forextrusion, can render the composition effectively extrudable and impartsurface smoothness to extruded parts thereof. One common method ofevaluating extrudability and extrudate properties involves mixing aceramic, typically cordierite with a small amount of ordinary Portlandcement and water, adding a conventional amount of a cellulose etherthereto, kneading the mixture, extruding the mixture, and examining theease of extrusion and the state of extruded parts. More particularly,100 parts by weight of a blend of 90 parts by weight of cordierite and10 parts by weight of ordinary Portland cement is mixed with 33 parts byweight of water, and 3 parts by weight of a cellulose ether is added tothe mixture. Immediately thereafter, the ingredients are kneaded at 20°C. and 20 rpm while a torque needed for kneading is measured. Thecellulose ether is evaluated to help kneading complete within a shorttime when the time taken until a maximum torque or torque peak isreached is fully short, typically within 180 seconds, from immediatelyafter the addition of cellulose ether. When a hydraulic composition iskneaded and extruded using such a nonionic water-soluble cellulose etherwhich enables brief kneading, extrusion can be carried out withoutfailures such as meander and breakage, and extruded parts havingimproved surface smoothness are available. The present invention ispredicated on this finding.

[0008] Accordingly, the present invention in one aspect provides anadmixture for extrudable hydraulic compositions, comprising a nonionicwater-soluble cellulose ether which is characterized in that when 3parts by weight of the nonionic water-soluble cellulose ether is addedto a mixture of 90 parts by weight of cordierite, 10 parts by weight ofordinary Portland cement, and 33 parts by weight of water, and theingredients are kneaded at 20° C. and 20 rpm immediately thereafter, amaximum torque for kneading is reached within 180 seconds from theaddition.

[0009] An extrudable hydraulic composition comprising the admixture isalso provided.

[0010] In a further aspect, the present invention provides a method forselecting a nonionic water-soluble cellulose ether suitable for use asan admixture for extrudable hydraulic compositions, comprising the stepsof adding 3 parts by weight of a nonionic water-soluble cellulose etherto a mixture of 90 parts by weight of cordierite, 10 parts by weight ofordinary Portland cement, and 33 parts by weight of water; immediatelythereafter kneading the ingredients at 20° C. and 20 rpm; measuring atime taken until a maximum torque for kneading is reached; and judgingthe nonionic water-soluble cellulose ether to be suitable when the timetaken until a maximum torque is reached is within 180 seconds from theaddition.

BRIEF DESCRIPTION OF THE DRAWING

[0011]FIG. 1 is a diagram showing how the kneading torque changes as anonionic water-soluble cellulose ether is dissolved.

DETAILED DESCRIPTION OF THE INVENTION

[0012] The admixture of the invention for extrudable hydrauliccompositions is defined as comprising a nonionic water-soluble celluloseether.

[0013] The nonionic water-soluble cellulose ethers which can be usedherein include alkyl celluloses, hydroxyalkyl celluloses, andhydroxyalkyl alkyl celluloses. Illustrative examples include, but arenot limited to, methyl cellulose, ethyl cellulose, hydroxyethylcellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose,hydroxyethyl ethyl cellulose and hydroxypropyl methyl cellulose.

[0014] Among these, an appropriate nonionic water-soluble celluloseether is selected which is characterized in that when 3 parts by weightof the nonionic water-soluble cellulose ether is added to a mixture of90 parts by weight of cordierite, 10 parts by weight of ordinaryPortland cement, and 33 parts by weight of water, immediately followedby kneading at 20° C. and 20 rpm, a maximum torque or torque peak forkneading is reached within 180 seconds from immediately after theaddition. When an admixture comprising an appropriate nonionicwater-soluble cellulose ether is used in a hydraulic composition, itbecomes possible to complete kneading of the hydraulic compositionwithin a short time, even with a reduced amount of nonionicwater-soluble cellulose ether, to provide a uniform hydrauliccomposition amendable to extrusion. The time taken until a maximumtorque or torque peak is reached is preferably within 120 seconds, andmore preferably within 60 seconds. If the time taken until a maximumtorque is reached exceeds 180 seconds, the kneading time must bemarkedly extended due to substantially retarded dissolution, which isinconvenient for practical manufacture.

[0015] The time taken until a maximum torque or torque peak is reachedis defined below. An experiment is carried out by using Labo PlastomillModel 30C150 (Toyo Seiki Seisaku-sho, Ltd.) equipped with a mixer havingan internal volume of 60 cm³ and a sigma shape blade S90B, feeding asample to the mixer, adjusting the temperature of the mixer and thesample at 20° C., kneading the sample at 20 rpm, and measuring a timepassed until a torque peak is reached. The sample used was prepared bypreviously thoroughly mixing 63 g of ready-mixed cordierite AF-2 (MarusuYuyaku Goshi Kaisha) and 7 g of ordinary Portland cement, adding 23.1 gof water thereto, thoroughly mixing and granulating the mixture, andadding 2.1 g of a nonionic water-soluble cellulose ether thereto. Thethus prepared sample is kneaded in the mixer under the above-describedconditions immediately after the addition of nonionic water-solublecellulose ether. From a profile of kneading torque change, a peak timeis determined. A zone of the profile where the torque rises correspondsto the duration when the nonionic water-soluble cellulose ether is beingswollen and dissolved while absorbing water, and a torque peak developsas a peak of partial dissolution. As dissolution proceeds further,plasticity is imparted to the kneaded mass and accordingly, the kneadingtorque decreases again. FIG. 1 is a diagram showing a profile ofkneading torque measured for the cellulose ether used in Example 2.

[0016] Preferably, the nonionic water-soluble cellulose ether has anaerated bulk density of 0.2 to 0.65 g/cm³, more preferably 0.2 to 0.4g/cm³. Also preferably, the nonionic water-soluble cellulose ether has aviscosity of 1,000 to 50,000 mPa.s, more preferably 1,500 to 50,000mPa.s, most preferably 3,000 to 50,000 mPa.s, as measured in a 1 wt %aqueous solution at 20° C. by a Brookfield viscometer at 12 rpm.

[0017] The nonionic water-soluble cellulose ether used herein isobtainable by properly selecting the type, substitution degree, bulkdensity, viscosity, average particle size, particle size distributionand other parameters of cellulose ether.

[0018] On use, the admixture of the invention comprising the nonionicwater-soluble cellulose ether, especially consisting of the nonionicwater-soluble cellulose ether alone or as a mixture of two or more isadded to an extrudable hydraulic composition. The amount of theadmixture added (the total amount of nonionic water-soluble celluloseethers) is an amount necessary to permit the hydraulic composition to beextruded, usually 0.1 to 2.0% by weight based on the entire componentsof the extrudable hydraulic composition excluding water, preferably 0.2to 2.0% by weight and more preferably 0.2 to 1.5% by weight.

[0019] If necessary, another water-soluble polymer may be used alongwith the admixture of the invention for extrudable hydrauliccompositions. Examples of other water-soluble polymers include partiallysaponified polyvinyl alcohol, modified starch, polyethylene oxide,wellan gum, and polyacrylamide.

[0020] The extrudable hydraulic composition of the invention containsthe admixture defined above as well as conventional components such ashydraulic substances, aggregates, lightweight aggregates, andreinforcing fibers.

[0021] The hydraulic substances that harden in the presence of waterinclude cement and gypsum. Cements include ordinary Portland cement,early-strength cement, blast furnace slag cement, fly-ash cement andalumina cement. Gypsum-based hydraulic substances include primarily thedehydrate, hemihydrate and anhydride forms of gypsum. The content ofcement or gypsum-based hydraulic substances is not critical and may beset as needed to achieve the required strength.

[0022] Powdered silica and fly ash are typical aggregates. Besides,lightweight aggregates are used when weight reduction is desired, andinclude perlite, hollow microspheres, and styrene beads. Whether theaggregate is ordinary or lightweight, it is combined with the hydraulicsubstance so that the desired properties are achievable. The hydraulicsubstance and the aggregate are used in a weight ratio of from 10:90 to100:0.

[0023] Reinforcing fibers are also useful in the hydraulic compositions.At present, pulp fibers that eliminate a concern about carcinogenicitybecome a substitute for asbestos and are widely used. In the practice ofthe invention, pulp fibers are advantageously used. Pulp fibers includefibers of virgin pulp, recycled paper pulp, and pulps originating fromconifer and broadleaf woods, having an average length of about 200 to2,000 μm. Polypropylene, vinylon and acrylic fibers are also useful.From the fire resistance and other standpoints, fibers are preferablyused in amounts of 1 to 10 parts by weight provided that the total ofthe entire components of the hydraulic composition excluding water is100 parts by weight.

[0024] If necessary, setting accelerators and retarders, and surfaceactive agents such as water-reducing agents and dispersing agents areused. These agents are effective for managing the physical properties ofa fresh hydraulic composition immediately after mixing of componentswith water. Any agent meeting a particular purpose may be added in aconventional amount.

[0025] To the hydraulic composition of the invention, water is added.The amount of water is conventional though it is determined inaccordance with the type of hydraulic composition or the like. Water ispreferably used in amounts of 20 to 80 parts by weight provided that thetotal of the entire components of the hydraulic composition excludingwater is 100 parts by weight.

[0026] The hydraulic composition of the invention is obtainable bymixing and kneading the aforementioned components in a conventionalmanner. The hydraulic composition thus obtained is formed and hardenedinto a hardened body by an extrusion molding or suitable method.

EXAMPLES

[0027] Examples of the invention and comparative examples are providedto illustrate the invention, and are not intended to limit the scopethereof.

Examples 1-3 and Comparative Example 1

[0028] Extrudable cement-based compositions formulated as shown in Table2 below were prepared from the following materials.

[0029] (1) Cement: ordinary Portland cement

[0030] (2) Silica: sifted silica powder

[0031] (3) Pulp: virgin pulp having an average fiber length of 0.8 mm

[0032] (4) Perlite: average particle size 0.8 mm

[0033] (5) Water-soluble cellulose ether: Four samples of methylcellulose were furnished. The time of torque peak upon dissolution inLabo Plastomill and viscosity of these samples are shown in Table 1. Thetorque peak time was measured by the procedure described above. TABLE 1Torque peak time and viscosity of water-soluble cellulose ether Torquepeak time Viscosity of 1 wt % aqueous solution Sample No. (sec) (mPa ·s) 1 20 2,000 2 54 12,800 3 171 5,400 4 205 7,200

[0034] The above materials other than water were mixed for 3 minutes ina Henschel mixer, and the prescribed amount of water was added.Immediately thereafter, the mixture was worked 4 minutes in a 10-literkneader-extruder, then extruded in vacuum. The parts extruded through adie of 6×75 mm profile were examined for extrudability and surfacesmoothness. The test results are shown in Table 2.

[0035] The evaluation criteria of these tests are shown below.

[0036] Extrudability: Visually Observed

[0037] ◯: no meander nor breakage

[0038] X: meander or breakage

[0039] Surface Smoothness: Visual Observation and Hand Feel

[0040] ◯: no apparent asperities, not rough to the feel

[0041] Δ: few apparent asperities, but rough to the feel

[0042] X: apparent asperities TABLE 2 Materials Example Comparative(pbw) 1 2 3 Example 1 Cement 45 45 45 45 Silica powder 30 30 30 30 Pulp5 5 5 5 Perlite 20 20 20 20 Cellulose ether No. 1 No. 2 No. 3 No. 4Cellulose ether amount 1.2 1.2 1.2 1.2 Water 45 45 45 45 ResultsExtrudability ◯ ◯ ◯ X (broken) Surface smoothness ◯ ◯ ◯ —

[0043] As is evident from Table 2, the hydraulic compositions ofExamples were effectively extrudable into hardened products havingimproved surface smoothness after the reasonable time of kneading. Incontrast, the hydraulic composition of Comparative Example 1 was brokenupon extrusion because of insufficient dissolution of the nonionicwater-soluble cellulose ether within the reasonable time.

[0044] The hydraulic composition to which a suitable amount of theinventive admixture is added can be kneaded within a brief time,obtaining a uniform kneaded mass which is smoothly extrudable.

[0045] Japanese Patent Application No. 2002-076058 is incorporatedherein by reference.

[0046] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. An admixture for extrudable hydraulic compositions, comprising anonionic water-soluble cellulose ether which is characterized in thatwhen 3 parts by weight of the nonionic water-soluble cellulose ether isadded to a mixture of 90 parts by weight of cordierite, 10 parts byweight of ordinary Portland cement, and 33 parts by weight of water, andthe ingredients are kneaded at 20° C. and 20 rpm immediately thereafter,a maximum torque for kneading is reached within 180 seconds from theaddition.
 2. The admixture of claim 1 wherein the nonionic water-solublecellulose ether is an alkyl cellulose, hydroxyalkyl cellulose orhydroxyalkyl alkyl cellulose.
 3. An extrudable hydraulic compositioncomprising the admixture of claim
 1. 4. A method for selecting anonionic water-soluble cellulose ether suitable for use as an admixturefor extrudable hydraulic compositions, comprising the steps of: adding 3parts by weight of a nonionic water-soluble cellulose ether to a mixtureof 90 parts by weight of cordierite, 10 parts by weight of ordinaryPortland cement, and 33 parts by weight of water, immediately thereafterkneading the ingredients at 20° C. and 20 rpm, measuring a time takenuntil a maximum torque for kneading is reached, and judging the nonionicwater-soluble cellulose ether to be suitable when the time taken until amaximum torque is reached is within 180 seconds from the addition.